This application claims the priority of German application 198 13 054.6-21, filed Mar. 25, 1998.
The invention relates to an airbag device for a motor vehicle with a housing in which an airbag that can be expanded suddenly through a housing opening is located. The housing opening is covered by a flexible protective cover when the airbag is in the resting state, said cover being provided with at least one tearing location, with the protective covering being so designed that it covers the airbag on all sides over at least a portion of its travel during expansion.
An airbag device of this kind is known from German Patent 39 10 337 C2, in which the airbag is stored in a housing, with two restraining tabs being fastened in each side of the housing. In the resting state of the airbag, these tabs are folded in the vicinity of the outlet opening over the latter. When the airbag expands, the restraining tabs are knocked out, so that they uncover the sides of the outlet opening opposite one another and thus are intended to avoid damage to the airbag during expansion.
In addition, an airbag device is known from European Patent Document EP 0 397 154 B1 for a motor vehicle. In this document, a housing of an airbag that can be inflated suddenly is sealed by a flexible protective cover made essentially in the form of a flexible cushion element made of plastic. The cushion element is permanently connected along its edge with a rigid frame and has a specified breaking location in the middle, where the cushion element is divided into two parts when the airbag inflates. These parts are pivotable laterally away from the direction of movement of the airbag.
An airbag device with an inflatable airbag is known from German Patent 196 31 556 C1, with a guide tube associated with the airbag. The guide tube is attached so that it cannot be lost, by an annular fastening area at one end to a housing of the airbag device or directly to the airbag itself. At the other end, it has a seam that is closed in the resting position and serves as a tearing location. The guide tube surrounds the airbag on all sides and in the resting position is folded around the airbag and/or the housing. When the airbag is inflated, the guide tube stretches and forms a firing channel in which the airbag expands. In the course of the expansion, the airbag tears the seam open at the end of the guide tube and emerges from the tube.
A goal of the invention is to provide an airbag device of the type recited at the outset which permits a uniform expansion of the airbag as well as improved protection against damage during the expansion of the airbag.
This goal is achieved according to the invention by the fact that the flexible protective cover is provided with two different tearing locations which are offset with respect to one another in the expansion direction in such fashion that the protective cover tears open in stages as the airbag expands. The tearing open of the tearing locations thus achieved is staggered in both time and space, producing a uniform extension rate of the airbag during the expansion, so that the load imposed on the occupant who comes in contact with the expanding airbag is minimized, especially in the initial phase of the expansion process. Furthermore, the protective cover forms a funnel- or tube-shaped guide for the airbag which prevents the airbag from snagging on parts or being braked by friction during expansion. Finally, the protective cover, by flanking the airbag at least partially on all sides, ensures that the airbag will not be damaged as it passes through the housing opening.
In an embodiment of the invention, the protective cover has an inner and an outer flat structure that are fastened at least approximately at right angles and offset with respect to one another at mounting positions on the housing that are opposite one another, with the inner flat structure covering the housing opening and being provided with a central tearing location in the form of a first tearing line, and with the outer flat structure being secured to fastening points that are offset at approximately right angles with respect to the fastening locations on the inner flat structure, having a second tearing line in a central area, and being stored folded in zigzag fashion in at least three layers. As a result, tearing open of the protective cover in stages during expansion of the airbag in an especially simple fashion is reliably guaranteed. The protective cover is divided by tearing lines, preferably aligned at right angles to one another, into at least four flat sections that are secured by one side to the housing, said sections overlapping the marginal area of the housing opening and largely covering the latter.
In another embodiment of the invention, a plurality of layers folded zigzag fashion are connected with one another by at least one fastening element. The fastening element, which can be made in particular as tearing threads sewn into a tearing seam, is either destroyed or pulled out of the protective cover during the expansion of the airbag, with the movement of the expanding airbag being braked in a deliberate and definable fashion.
In another embodiment of the invention, the outer and inner flat structures are integrated in a common material section, with the outer flat structure being folded at right angles to the inner flat structure. As a result, the entire protective cover can be manufactured in simple fashion from a material web so that the outer and inner flat structures can be aligned reliably and accurately with respect to one another.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.